Disc-shaped recorded media, for example an optical disc or a magneto-optical disc, utilizing the method of optical or magneto-optical signal recording and reproducing, are well known in the art. The various types of such disc-shaped recording media include: (1) recording media of the read-only-memory (ROM) type, e.g., an audio compact disc (CD) or a CD ROM, (2) write-once type recording media on which data can be written only once by the user, and (3) overwrite type recording media, such as a magneto-optical disc, on which data re-recording is possible. Other well known examples of optical recording media are video CDs, CD-I, CD-MO, MD, etc.
In order to mass produce optical discs a master disc is produced through a mastering process. This mastering process involves a basic sequence of processing steps. The sequence starts with providing a circular glass substrate that must be cleaned and dried and then carefully inspected for imperfections, surface smoothness and the like. An adhesive coating layer is then placed on one surface of the glass to exacting tolerances. The adhesive coating layer is followed by a photoresistive coating layer evenly and continuously applied over the adhesive layer over the entire glass substrate surface.
The glass substrate must then be appropriately cured, after which recording with an optical beam takes place. The recording process involves selectively exposing the photoresistive coating to a beam of light from a light source in order to form the appropriate pattern of pits and lands which represent the data recorded on the disk. If the light source is a laser, it is typically of a continuous wave type, with exposure of its beam to the photoresistive coating conventionally controlled by an acousto-optical modulator (AOM).
The AOM acts as an electronic shutter to the laser beam and, as is well-known by those skilled in the art, is controlled by a string of binary 1's and 0's generated by an encoder. The encoder converts, for example, stereo audio signals typically recorded digitally on a tape in a video or audio format to the appropriate binary 1's and 0's by performing eight-to-fourteen modulation (EFM). As part of this encoding, the encoder generates so-called RS parity bytes and adds merging bits.
After the photoresist has been selectively exposed to the laser, the photo-resistive coating must be developed so that the exposed portions can be removed. Developing is accomplished by placing the substrate in a caustic sodium hydroxide solution. After developing, the glass must be inspected by measuring, among other things, the diffraction orders of the tracks.
The next step, metalization, involves placing a thin coating of silver or nickel over the entire surface of the substrate. This metalization cover follows the pattern of pits and lands of the now developed photo-resistive layer. In the case of silver, the metalization step is accomplished by a well known evaporation process resulting in the formation of a metal coating typically 120 nanometers thick. At this point, the metalized substrate, or the "glass master," is typically "played" in a specially adapted CD player to insure that the pits have been properly formed.
A nickel plating is then formed via electroplating over the metalized glass substrate such that a metal master is formed when the nickel plating is removed from the substrate. The metal master has pits and lands which are the inverse of those on the metalized glass plate. This metal master is called a "father" and is created by well-known electroplating procedures. Because the extremely thin silver or nickel metalization forming the glass master adheres to and is removed with the nickel plating of the father, there can only be one father.
From the metal master or father, a so-called "mother" is formed, also out of nickel. The mother is simply the inverse of the metal master or father and is similarly formed by electroplating. Several mothers can be formed from the metal master or father.
Finally, nickel stampers are formed from the mothers. The stampers carry the pattern of the father and are again simply the inverse of the mother. Nickel stampers are formed by electroplating a mother in the same way a mother is formed from the father. From the stampers, compact discs can be manufactured by injecting molten molding resin, e.g., optical quality polycarbonate, at high pressure into a mold comprising the stamper and allowing it to solidify.